Synthesis of bimetallic 4-PySI-Pd@Cu(BDC) via open metal site Cu-MOF: Effect of metal and support of Pd@Cu-MOFs in H2 generation from formic acid

Article abstract of DOI:10.1016/j.mcat.2019.01.031

Catalysts based on palladium ions grafted on Schiff-base decorated OMS-Cu(BDC) pore cage were prepared and their catalytic performance in the hydrogen generation from formic acid was studied. The effects of the porous MOF structure and Schiff-based group

Full text of DOI:10.1016/j.mcat.2019.01.031

Molecular Catalysis 467 (2019) 30–37
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Synthesis of bimetallic 4-PySI-Pd@Cu(BDC) via open metal site Cu-MOF:
Effect of metal and support of Pd@Cu-MOFs in H generation from formic
2
acid
Hassan Alamgholilooa,1, Shengbo Zhang , Arefeh Ahadi , Sadegh Rostamnia , Reza Banaei ,
Zhongcheng Li , Xiao Liu , Mohammadreza Shokouhimehr
c,1
a
a,⁎
a
d
b,⁎
e,⁎
a
Organic and Nano Group (ONG), Department of Chemistry, Faculty of Science, University of Maragheh, PO BOX 55181-83111, Maragheh, Iran
Key Laboratory of Pesticide & Chemical Biology of the Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, 430079, China
Key Laboratory for Green Chemical Technology, School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China
State Key Lab Base of Eco-chemical Engineering, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao, 266042,
b
c
d
China
e
Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bimetallic metal-organic framework
Pd@Cu-MOFs
Formic acid dehydrogenation
Heterogeneous catalysis
Catalysts based on palladium ions grafted on Schiff-base decorated OMS-Cu(BDC) pore cage were prepared and
their catalytic performance in the hydrogen generation from formic acid was studied. The effects of the porous
MOF structure and Schiff-based group presented around the Pd ions play important roles in stabilizing the Pd
ions, providing strong interaction between the MOF support and Pd site. The Pd-Schiff base complex grafted on
Cu-MOF exhibits excellent catalytic activity to produce 147 mL of gas (H
2
+ CO
2
) with the turnover frequency
−
1
(TOF) value of 412 h towards the dehydrogenation of formic acid without any additives. The heterogeneous
molecular catalyst could be easily recycled through the filtration and almost has no activity loss during the reuse.
The results revealed that the heterogeneous Pd-based Cu-MOF is a promising catalyst for the hydrogen gen-
eration from formic acid.
1. Introduction
FA is one of major products of biomass processing vehicles that has
been regarded as a convenient and safe hydrogen storage material be-
In recent years, with the increased consumption of fossil fuels and
cause of its easy rechargeability, high stability, nontoxicity and high H
content (4.4 wt%) [7–9]. The decomposition of FA follows two prin-
cipal pathways: One process generates CO and H via dehydrogenation
(1), and other produces CO and H O via dehydration (2), as shown
below [9,10,11]. Reaction (2) is undesired because one of its product,
CO, is detrimental to the catalysts used in many fuel cell and besides
2
growing environmental problems, alternative green and clean energy
sources have been attracting considerable attention [1–3]. Among the
various alternative energy strategies, hydrogen energy is regarded as
one of the most promising renewable and green energy sources in a
2
2
2
number of fields [2,4]. One potential application of H
especially for fuel cell vehicles (FCVs), to replace the fossil fuels and
contribute to the development of zero CO emission technology due to
2
is as the fuel
2
does not generate the desirable product H .
2
48.8 kJ mol−1
−
−
HCOOH (l)
HCOOH (l)
→
→
CO
2
(g) + H
2
(g) Δ G298K
=
=
(1)
(2)
its high gravimetric energy density and non-toxicity [5]. However, most
of the hydrogen employed today is supplied from coal gasification and
steam reforming. It is highly required to explore more mild and man-
oeuvrable ways for hydrogen generation using alternative technologies.
Recently, formic acid (HCOOH, FA) has been considered as a po-
−1
CO (g) + H O (l) Δ G
2
298K
28.5 kJ mol
Many studies have shown that metal nanoparticles can efficiently
catalyze FA decomposition to produce hydrogen. Asefa and co-workers
have proposed a series of mesoporous silica materials of SBA-15 family
for the immobilization of Pd nanoparticles and catalytic properties to-
ward FA dehydrogenation are elucidated [12]. Mori and Yamashita
tential liquid storage material capable of releasing H
2
under mild
condition via catalytic decomposition process [6]. On the other hand,
⁎
Corresponding authors.
E-mail addresses: rostamnia@maragheh.ac.ir (S. Rostamnia), liuxiao71@tju.edu.cn (X. Liu), mrsh2@snu.ac.kr (M. Shokouhimehr).
H. Alamgholiloo and S. Zhang contributed equally.
1
https://doi.org/10.1016/j.mcat.2019.01.031
Received 2 November 2018; Received in revised form 23 January 2019; Accepted 24 January 2019
2468-8231/ © 2019 Elsevier B.V. All rights reserved.

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
synthesized PdAg nanoparticles on phenylamine-functionalized meso-
porous silica or carbon, which can act as useful catalysts
2. Results and discussion
for the H
Pd-based bimetallic and multi-metallic alloy and composite materials
such as Pd-MIL-125 [17], Au@Pd/UiO-66(Zr Ti ) [18], Ag-Pd/rGO
19], PdNiAg/C [20], Ag-Pd core-shell nanocatalyst [21], Au@Pd/N-
mrGO [22], Pd/mpg-C [23], PdCoNi/TiO [24], AgPd@ZIF-8 [25]
and Au-Pd/MIL-101 [8] have also been developed as heterogeneous
catalysts for dehydrogenation of FA. Compared with metal nano-
particles, homogeneous metal complex catalysts have much higher
catalytic activity. For example, Xiao et al. defined cyclometalated ir-
idium (III) complexes based on 2-aryl imidazoline ligands and de-
2
delivery mediated by formic acid [13–16]. In addition,
The secondary building unit (SBU) of Cu(BDC)∙nDMF consists of a
dimeric copper unit that is bridged by four carboxylate functionalities
of four H BDC molecules [33]. Each copper atom is cubically co-
2
ordinated by four oxygen atoms and the remaining open metal site, in
the as-prepared form occupied by a solvent molecule like DMF, re-
presents the possible active site for catalytic transformations [36].
Herein, in our current method, the Cu(BDC)∙nDMF was prepared by
x
y
[
3
N
4
2
2
using copper nitrate and H BDC as ditopic ligand in room temperature
conditions, which was then activated under thermal/vacuum condi-
tions to obtain open metal site Cu(BDC) solid [OMS-Cu(BDC)]. This
OMS-MOFs reacted with as-synthesized 2- and 4-pyridylsalicylimine
(PySI) moiety through the coordination with PySI Schiff-base to form
unsaturated metal/cluster site of activated Cu(BDC). Afterward,
2 3
monstrated catalytic application for the decomposition of HCO H-NEt
−
1
2
mixture to give H with high turnover frequency of 147,000 h under
mild conditions [26]. However, homogeneous catalysts usually suffer
from deactivation caused by intermolecular pathways, leading to the
low durability. How to combine the merits of homogeneous catalysts
with high activity and heterogeneous catalysts with high durability for
the efficient FA dehydrogenation still remains an attractive goal.
The immobilization of homogeneous metal complex onto solid
supports is a common method to fabricate heterogeneous molecular
catalysts. Among various type of solid catalysts, transition metal com-
plexes supported on metal-organic frameworks (M@MOFs) represent
one of the most important groups [25,27], owing to their advantages
such as high surface area, defined pore size, tunable structure in their
framework [28,29]. MOFs and open metal site MOFs (OMS-MOFs) are
also ideal platforms for post-synthetic modification (PSM) chemistry to
achieve multi-purpose materials [30], especially OMS-Cu-MOFs such as
Cu(BTC) and Cu(BDC) [31–33].
2
through the postsynthetic metalation of PySI@Cu(BDC) with PdCl ,
heterogeneous solids 4-PySI-Pd@Cu(BDC) and 2-PySI-Pd@Cu(BDC)
were obtained with the Pd contents of 0.8 wt% and 0.78 wt% measured
by atomic absorption spectroscopy (AAS), respectively, (Scheme 1).
The synthesized Cu(BDC) and PySI-Pd@Cu(BDC) were checked by
powder X-ray diffraction (PXRD) measurement (Fig. 2). The results
demonstrate that the peak positions matched well with that of the si-
mulated diffraction pattern [37]. In our MOFs, a sharp peak below 2 θ
= 10.27° indicated a crystalline OMS-Cu(BDC) structure based on lit-
erature comparison [38]. A comparison of the PXRD pattern of 4-PySI-
Pd@Cu(BDC) with OMS-Cu(BDC) revealed a shift to smaller 2 θ angles
for the main peak (220), although other main diffraction peaks showed
some slight decreases of peak intensities with the immobilization of Pd-
Schiff-based complex, due to the partial filling by the grafting guest
molecules.
Recently, we have reported the catalytic application of OMS-MOFs
of Cu-MOFs belonging to terephthalic and trimesic acid in chemical
transformations [34,35]. To screen out efficient heterogeneous Pd-
based precatalyst for FA dehydrogenation process using commercial
available compounds, we herein report the complexation of single-site
Pd space onto the Schiff-base grafted on pore cage of OMS-Cu(BDC).
And then, the synergistic effects of metal and two kinds of Schiff-base
ligands grafting onto the MOF cluster framework for the catalytic de-
hydrogenation of FA were studied. The resultant of Pd@Cu(BDC) with
more open active site exhibits excellent catalytic activity with the
FT-IR spectra were implemented to investigate the chemical struc-
tures of synthesized Cu(BDC)∙nDMF, 4-PySI@Cu(BDC) and 4-PySI-
Pd@Cu(BDC) in Fig. 3. The FT-IR spectrum of the Cu(BDC)∙nDMF was
compared with the samples after Shift-base ligand and Pd grafting. As
−
1
for Cu(BDC)∙nDMF, the strong peaks at 1396 cm
symmetric and
−1
1623 cm
asymmetric vibration are corresponding to carboxylate
presence in the MOF [34]. The bonds at 1507 cm and 2971 cm are
−
1
−1
assigned to C]C in aromatic ring of BDC and aliphatic CeH of co-
ordinated DMF and CeH of aromatic rings of BDC. A new peak at 3357
−
1
−1
turnover frequency (TOF) value of 412 h , and 147 ml of gas (H
CO ) was obtained within three hours toward dehydrogenation of FA
Fig. 1).
2
and
cm
in 4-PySI@Cu(BDC) and 4-PySI-Pd@Cu(BDC) shows the fre-
2
quency of the OeH group of the 4-PySI ligand in MOFs, demonstrating
the grafting of 4-PySI ligand onto copper (II) CUSs in the cages of the Cu
(
(
BDC). The FT-IR of 4-PySI-Pd@Cu(BDC) demonstrates that the
Fig. 1. Synthetic pathway of 4-PySI-Pd@Cu(BDC) vs. 2-PySI-Pd@Cu(BDC).
31

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
Scheme 1. Schematic illustration for the preparation of PySI-Pd@Cu(BDC).
The FE-SEM result of the 4-PySI-Pd@Cu(BDC) shows its high stability of
the structure and morphology even after multi-step post-modifications.
Fig. 5a shows a dark-field STEM micrograph of the post-synthetic
modified OMS-Cu(BDC) to 4-PySI-Pd@Cu(BDC) compound, indicating
a typical truncated cubic morphology. The STEM-EDS mapping images
in Fig. 5b proved the presence of C, O, N, Cl, Cu and Pd elements in the
4-PySI@Cu(BDC) structure. The collected data from energy dispersive
X-ray (EDX) analysis of the OMS-Cu(BDC), 4-PySI@Cu(BDC) and 4-
PySI-Pd@Cu(BDC) are shown in Fig. 5c. Based on this analysis, copper,
carbon and oxygen atoms exist in the structure of OMS-Cu(BDC), which
indicates the high purity and perfect activation of Cu-MOF solids. The
appearance of N-atoms in EDX of 4-PySI@Cu(BDC) demonstrates the
successful salicylimine Schiff-base (4-PySI) coordination onto the OMS-
Cu(BDC). Finally, Pd and Cl atoms in 4-PySI-Pd@Cu(BDC) indicate
palladium chloride complex were successfully grafted onto the Schiff-
base decorated OMS-Cu(BDC) pore cage.
Fig. 2. PXRD patterns of the OMS-Cu(BDC), 4-PySI@Cu(BDC).and 4-PySI-
Pd@Cu(BDC).
The porosity properties of the OMS-Cu(BDC) and 4-PySI-Pd@Cu
(
BDC) were determined by nitrogen adsorption-desorption test after
being heated under vacuum at 120 °C. The N adsorption-desorption
2
isotherms in Fig. 6a and b represent a typical I related to microporous
materials. The presence of Pd complex inside the pore cage of Cu-MOF
is evidenced with a simultaneous decrease of the micropore surface
3
3
areas [from 340 cm /g for OMS-Cu(BDC) to 210 cm /g 4-PySI-Pd@Cu
BDC)].
In order to investigate the thermal stability of Cu-BDC∙nDMF and 4-
PySI-Pd@Cu(BDC), thermal gravimetric (TG) analysis was conducted
Fig. 7). From the performed results, three steps of weight loss were
(
(
observed and the two solids show a similar thermal behavior. The first
step of weight loss before 200 °C was attributed to the loss of adsorbed
toluene and DMF from the MOF surfaces, and weight loss between
230–250 °C was attributed to the DMF molecules coordinated with Cu.
Sharp decrease in weight at 255–370 °C indicates that the phase was
completely changed. The MOF structure was decomposed in the beyond
4
00 °C and the result of TGA analysis demonstrates that our MOF is
thermally stable up to 230 °C. The overall powder X-ray diffraction
PXRD) and thermal stability of Cu-MOF were in good agreement with
(
Fig. 3. FT-IR spectrum of Cu(BDC)∙nDMF (black), 4-PySI@Cu-BDC (green) and
the literature [39].
4-PySI-Pd@Cu(BDC) (red). (For interpretation of the references to colour in this
The FA dehydrogenation reaction was then carried out by placing
the series of Pd@Cu-MOFs of 4-PySI-Pd@Cu(BDC) and 2-PySI-Pd@Cu
figure legend, the reader is referred to the web version of this article).
(
BDC) in 5 mL of 5% of FA at room temperature. GC analysis showed
structure did not change considerably after attachment of the Pd (II)
ions onto the Cu(BDC) pore cage.
the volume ratio of H to CO is 1 and no CO gas was generated. Fig. 8
2
2
illustrates time-dependent kinetic curves of different catalysts under the
same reaction conditions within 3 h. With the increasing of the reaction
time, total gas amounts were linearly increased at the beginning and
gradually reached to the highest level after 2 h. 4-PySI-Pd@Cu(BDC)
exhibited higher catalytic activity compared with the catalyst 2-PySI-
Pd@Cu(BDC) without the use of any additives. Within 3 h, about
Field emission scanning electron microscopic (FE-SEM) analysis of
the Cu(BDC)∙nDMF and 4-PySI-Pd@Cu(BDC) are shown in Fig. 4. It can
be seen that Cu(BDC)∙nDMF and the modified PySI@Cu-BDC revealed
the presence of cubic assembled layered microcrystals and the particles
are uniform and ordered in size (Fig. 4a–c). After the postsynthetic
metalation with Pd, the morphology was almost maintained (Fig. 4d).
32

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
Fig. 4. a, b) FE-SEM images of Cu(BDC) and its lateral surface. c) 4-PySI@Cu(BDC) and d) 4-PySI-Pd@Cu(BDC).
Fig. 5. a) STEM image and b) STEM-EDS elemental mapping of 4-PySI-Pd@Cu(BDC). c) EDX analysis of OMS-Cu(BDC), 4-PySI@Cu(BDC) and 4-PySI-Pd@Cu(BDC).
33

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
2
Fig. 6. a) N adsorption-desorption isotherm of the a) OMS-Cu(BDC) and b) 4-PySI-Pd@Cu(BDC).
1
47 mL of H
2
and CO
2
was generated for 4-PySI-Pd@Cu(BDC) with the
∙nDMF and OMS-Cu(BDC) was almost catalytic inactive. The catalytic
activity increased after the multi-step grafting of palladium Schiff-base
complex. When PySI was coordinated with OMS-Cu(BDC), 4-PySI@Cu
−
1
TOF of 412 h . Meanwhile, 2-PySI-Pd@Cu(BDC) gave 125 mL of H
and CO with the TOF of 315 h . For 4-PySI-Pd@Cu(BDC), Pd active
2
2
−
1
−
1
site is much easier to be reacted with the reactant than that of 2-PySI-
Pd@Cu(BDC), due to the more open active site deriving from the para
position of the coordination bond of Cu with aminopyridine. These
results indicate the high effects of the Schiff-base ligand 4-PySI com-
pared with 2-PySI in stabilizing and keeping the Pd in active state in the
Cu-MOF structure.
(BDC) produced about 40 mL of H
After the immobilization of Pd, 4-PySI-Pd@Cu(BDC) gave 147 mL of H
and CO
2
and CO
2
with the TOF of 126 h
.
2
2
. The results clearly demonstrate that the effect of chelating
ligand and Pd metal in comparison of the copper in Cu-MOF structure,
which may have synergetic effect between Pd metal and Schiff-base
group to improve the dehydrogenation of FA.
We further compared the activity of our catalysts with the reported
ones (Table 1). It can be seen that 4-PySI-Pd@Cu(BDC) with the TOF of
The influence of various catalyst amounts on the catalytic perfor-
mance of the PySI-Pd@Cu(BDC) were investigated and the results were
shown in Fig. 10. With the increasing of the catalyst amount from 1 to 5
to 10 mg, the TOF value of 4-PySI-Pd@Cu(BDC) was gradually in-
creased from 290 to 386, then to 412 h . When 15 mg of the catalyst
was used, the activity has almost no change. The change of the TOF
with the different amount of catalyst might demonstrate the existence
of cooperative effects among the active sites. When more solid catalysts
were used, the possibility of the interactions among different catalytic
sites was increased and the cooperation resulted in the accelerated re-
action rate.
−
1
412 h at 293 k is superior to most of the reported catalysts (Entry 1 in
Table 1), although it is still lower than those of Ag18Pd82@ZIF-8 and
PdNi/GNs-CB (Entry 10, 12). The high activity of 4-PySI-Pd@Cu(BDC)
could be attributed to the unique effects of the Schiff-base ligand 4-PySI
in stabilizing and keeping the Pd in open active state in the Cu(BDC)
structure.
Catalytic performance and synergistic effect of Pd metal in the
framework structure of Cu-MOF were studied based on the amount of
generated gases and TOFs during the reaction. Their catalytic activities
were strongly depended on the Pd Schiff base (Fig. 9). The Cu(BDC)
−
1
The reusability of Pd@Cu-MOFs was tested by performing repeated
Fig. 7. TG analysis of the Cu-BDC∙nDMF (brown line) and 4-PySI-Pd@Cu(BDC) (green line). (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article).
34

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
2 2
Fig. 8. FA dehydrogenation over as-synthesized catalysts: a) volume of the product gases (H and CO ) and b) catalytic TOF of the reaction.
Table 1
Comparison of activities of different catalysts for hydrogen generation of FA.
Entry
Catalyst
T (K)
TOF (h−1)
Ref.
1
2
3
4
5
6
7
8
9
4-PySI-Pd@Cu(BDC)
2-PySI-Pd@Cu(BDC)
AuPd@ED-MIL-101
Ag@Pd
Ag/Pd alloy
Pd-Au-Eu/C
293
293
363
293
293
363
298
298
333
353
353
298
298
323
323
323
365
412
315
106
125
144
387
382
80
This work
This work
[8]
[21]
[21]
[40]
[41]
[42]
[43]
[25]
[44]
[45]
[46]
[47]
[48]
[48]
[49]
AuPd-MnO
X
/ZIF-8-rGO
Co0.30Au0.35Pd0.35
Pd/C
Ag18Pd82@ZIF-8
79
10
11
12
13
14
15
16
17
580
312
529
64
382
80
PtRuBiO
X
PdNi/GNs-CB
Pd/C with citric acid
Ag42Pd58/C
Au/C
Au41Pd51/C
230
113
Fig. 10. The effect of various catalyst amounts on the dehydrogenation of FA.
PdAu/C-CeO
2
with DI-water for several times and then dried in an oven/vacuum in
120 °C. As shown in Fig. 11, the activity was almost kept for at least
three times, suggesting that the Pd@Cu-MOFs was stable during the
dehydrogenation of FA for a long time (Fig. 12). XRD further testified
reaction cycle using 10 mg of 4-PySI-Pd@Cu(BDC) and 2-PySI-Pd@Cu
BDC) under the same reaction condition. The catalysts after each re-
action was recovered and reactivated by common filtration, washed
(
2 2
Fig. 9. Effect of metal in structure of Cu-MOF in dehydrogenation of FA: a) volume of the product gases (H and CO ) and b) TOF values of different samples.
35

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
Fig. 11. a) Recycling test for FA dehydrogenation catalyzed by 1 and 2 at room temperature. b) XRD analysis after the 3rd recycling of 4-PySI-Pd@Cu(BDC).
Fig. 12. XPS spectra of (a) 4-PySI-Pd(II)@Cu(BDC) and (b) 4-PySI-Pd(0)@Cu(BDC).
the stable structure of the solid catalyst after the reuse.
640 spectrometer, absorbencies are repotted in cm−1. SEM images of
the samples were recorded with a Zeiss-DSM 960 A microscope. TEM
images were obtained by using a Zeiss EM 900 electron microscope. The
The electronic state of Pd species in MOF samples of as-synthesised
4-PySI-Pd@Cu(BDC) and 3rd recycling of 4-PySI-Pd@Cu(BDC) were
also further analysed by the X-ray photoelectron spectroscopy (XPS). As
CO
analyzed quantitatively by a gas chromatograph equipped with a
thermal conductivity detector (TCD) and compared it by automatic H
and CO gas measuring device. For the recycling catalytic performance,
after every run, the MOF catalyst was recovered by simple centrifuge
(14,000), dried/vacuumed and reused.
2 2
and H molecules generated in the reactor set up were periodically
(
II)
shown in Fig. 12a for as-synthesized 4-PySI-Pd @Cu(BDC), two well
defined peaks with binding energies of 337.88 and 343.18 eV are ob-
served, which can be related to the signals of 3d5/2 and 3d3/2 levels of
Pd(II) components, respectively. After 3rd recycling of 4-PySI-Pd@Cu
2
2
(
BDC), during the FA decomposition process, H
of Pd(II) to Pd(0) and XPS scan indicate two signal at 337.08 and
42.38 are attributable to palladium metallic Fig. 12b. For both sample
2
generated a reduction
3
3.2. Synthesis and activation of Cu(BDC)∙nDMF [OMS-Cu(BDC)]
(
0)
of 4-PySI-Pd@Cu(BDC) and 4-PySI-Pd @Cu(BDC), the binding energy
BE) difference of the two peaks is 5.3 eV, which is in accordance with
the theoretical value. [50,51]
(
The synthesis of Cu(BDC)∙nDMF was carried out following the room
temperature synthesis method reported by our group and the literature
references [34]. In a typical preparation, equimolar quantities of Cu
(
1
NO
3 2 2 2
) ∙3H O (7.5 mmol, 1.812 g) and H BDC (7.5 mmol, 1.245 g) in
3. Experimental
50 mL DMF for 8 h were used. After synthesis, the blue precipitated
was collected by centrifugation, and washed three times with DMF. To
remove residual unreacted ions and terephthalic acid, the as-synthesis
3.1. Chemicals and apparatus
2 2
Cu(BDC)∙nDMF was purified with hot methanol and CH Cl for 4 h, and
2 3 2 2
Benzene 1,4-dicarboxylate (H BDC), Cu(NO ) ∙3H O, 4-aminopyr-
idine, 2-aminopyridine and other compounds and reagents were ob-
tained commercially from Sigma-Aldrich, Merck (Germany) and Fluka
then it was filtered and dried at 60 °C under vacuum overnight. Finally,
Cu(BDC)∙nDMF was activated at 393 K under vacuum to obtain open
metal site OMS-Cu(BDC) MOF.
(
Switzerland), they were used without further purification. The crys-
talline phases of the MOF material were recognized by XRD measure-
ments (Philips-PW 1800 diffractometer). The palladium content of the
MOFs were measured by atomic absorption spectroscopy (AAS). Fourier
transform infrared (FT-IR) spectra were obtained using a Shimadazu IR-
3.3. Preparation of 4-PySI@Cu(BDC) and 2-PySI@Cu(BDC)General
First, 1 g of Cu(BDC)∙nDMF was activated at 393 k under vacuum to
36

H. Alamgholiloo et al.
Molecular Catalysis 467 (2019) 30–37
obtain a dark-violet OMS-Cu(BDC) solid. In a dried balloon 4-amino-
pyridine (1 mmol) and salicylaldehyde (1 mmol) was reacted in solvent-
free condition at 90 °C. Then the mixture of salicylimine (SI) and OMS-
Cu(BDC) was added to each other in 15 mL of dry toluene and the
suspension was heated again at 90 °C for 12 h. The 4-PySI@Cu(BDC)
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was separated by centrifugation, washed with CH
73 K overnight. The same recipe was done for 2-PySI@Cu(BDC) with
replacing 2-aminopyridine instead of 4-aminopyridine.
2 2
Cl and dried at
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3.4. procedure for synthesis of compound X
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Acknowledgements
[
1
We acknowledge the National Natural Science Foundation of China
U1662109) and Iran National Science Foundation (INSF) for financial
support. The Program of Introducing Talents of Discipline to
Universities of China (111 program, B17019) is also acknowledged.
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